The pol gene of HIV encodes three key enzymes for viral replication. Two of these enzymes, HIV reverse transcriptase (RT) and HIV protease; have received considerable attention in terms of clinically useful inhibitors. In contrast, the third enzyme of the pol gene, HIV integrase, has received much less attention. There are no drugs in clinical use for AIDS where the mechanism of action is inhibition of HIV integrase. The integration process is essential for HIV replication and there is no functional equivalent of HIV integrase in human cells. It is clear that new information on inhibitors of this enzyme is of critical importance in the anti-HIV drug discovery area. The long-term objectives of this research project are the discovery of therapeutically useful inhibitors of HIV integrase. Utilizing knowledge on the mechanism of action of HIV integrase, two potent inhibitors of HIV-1 integrase have been discovered in the current grant period . These inhibitors are conceptually novel dinucleotides that are recognized by HIV integrase and that inhibit both the 3'-processing and strand transfer steps involved in the incorporation of viral DNA into human DNA. In addition, these compounds exhibit resistance to degradation by nucleases. If this were not to be the case, these molecules would not be of therapeutic significance. This renewal proposal moves the project into the next phase of development which includes both new synthesis and comprehensive in vitro anti-HIV studies of nuclease-resistant, sequence-specific dinucleotides and their pro-drugs that are stereochemical and regiochemical analogs of the newly discovered inhibitors. One goal of the proposed work is to increase the activity (IC50) against integrase from the low micromolar into the nanomolar range, which would be therapeutically very significant. The planned in vitro anti-HIV studies include wild-type HIV and drug- resistant HIV isolates, as well as drug combination studies. It should be stated that correlation of nucleoside stereochemistry with inhibition of HIV reverse transcriptase by the corresponding triphosphates led to the discovery of some clinically useful anti-AIDS agents. Related reasoning and current data strongly suggest that conformational and configurational factors, as well as base sequence recognition, may be of critical importance in the discovery of therapeutically significant anti-AIDS dinucleotides that are directed at HIV integrase. This is a significant focus of the current proposal.